Stretch leveling machine



Sheet of 2 June l0, 1969 E. H. BRAUER STRETCH LEVELING MACHINE Filed Feb. s, 1967 INVENTOR. 14M 0% @rw-ab,

June1o,19e9, l E .HBRAUR 3,448,603

STRETCH LEVELING MACHINE l Filed Feb. s, 1967 sheet of 2 INVENTQR.

\ AT TGRNEY.

United States Patent O U.S. Cl. 72-296 6 Claims ABSTRACT OF THE DISCLOSURE The machine comprises a frame on which a die support is mounted for vertical movement and is raised and lowered by a power cylinder. Stretch heads are pivotally mounted on the frame at opposite ends of the die support for rocking about horizontal axes extending forwardly and rearwardly of the frame. Rock levers are mounted on the frame for rocking about axes parallel to those of the heads, respectively. Each rock lever is connected by a link at one side of its rocking axis to its associated head and is drivingly connected by a link at the opposite side of its axis to the power cylinder so that the stretch heads are rocked away from each other upon raising of the die by the power cylinder.

This invention relates to an improved sheet stretching machine, and particularly to a machine for stretch leveling sheets preparatory for forming them in presses and the like.

It is desirable that the sheet stock be caused to engage flatwise with the crest or central portion of a bridge or table surface which has a slightly higher portion positioned usually midway between the ends of the sheet stock. The sheet engaging surface of such portion is generally lineal in section transversely of the tensioning dimension and slightly curved and convex toward the stock in section longitudinally of the tensioning dimension. Having engaged the sheet with this portion, the sheet is tensioned unidimensionally endwise. The purpose of engaging the sheet with the bridge before tensioning is to eliminate an effect called fluting, which is a formation of wrinkles which generally extend predominantly endwise of the sheet, often entirely from one end to the other, and which tend to diverge transversely of the sheet from the mid-portion of the sheet toward the ends of the sheet.

After the sheet has first engaged the bridge firmly near such mid-portion, it can be stretched endwise, or in a direction transversely of the length of the bridge, to a flat condition without the formation of flutes. The ends of the sheet generally are pulled also normal to the plane of the sheet in the crest engaging direction so that the end portions slope downwardly from the crest in each direction endwise of the sheet. The angle of slope is so slight that the sheet, if laid on a flat surface with the convex face upwardly, will flex under its own weight and become flat and planar.

One problem, however, is to provide a simple and effective stretching machine for stretching sheets in this manner and for assuring engagement of the sheet and bridge before stretching. This is accomplished by a simple and compact machine which is illustrated in the following drawings wherein:

FIG. l is a top plan view of the machine embodying I the principles of the present invention, part thereof being shown in section for clearness in illustration; and

FIG. 2 is a front elevation of the machine illustrated in FIG. 1, part thereof being shown in section for clearness in illustration.

-For brevity in describing and claiming the portions and movements of the parts of the machine relative to each other, the machine is described in an upright posi- ICC tion, and the positions and movements of the parts are described in relation to this position which is not absolute.

The machine comprises essentially a rigid box-like frame 1 having a supporting base plate 2 and at the top a table 3 above which is a bridge or die 4 over which metal sheets are to be stretched. For stretching the sheets unidimensionally, two gripping heads 5 for gripping two opposite margins are mounted on the frame 1 for movement relatively toward and away from each other.

Each head comprises a fixed jaw `6 and a movable jaw 7 pivotally connected by a pivot -8 to a support 9. Suitable piston and cylinder assemblages 10 are provided for opening and closing the jaws by rocking the jaw 7 about the pivot 8. For this purpose, Ithe piston 10 carries a trunion 11 which is -connected to links 12, which upon movement of the cylinder away from the support 9, moves the jaws t0 clamping position. The cylinder carries a piston having a rod 13 which is connected to the support 9.

A plurality of such assemblages and linkages may be provided, depending upon the wid-th of the sheet, the cylinders thereof being connected in parallel to a hydraulic source and controlled by conventional reversing valves, or connected to an air line through suitable air line inlet and exhaust valves.

It is desirable in loading a sheet between the jaws that -the sheet be loaded without being supported or stretched across the top of the bridge or die over which the sheet is to be stretch leveled. For this purpose, the bridge or die 4 is connected by means of a pivot 15 on yoke 16 to the rod 17 of a piston 18 which is reciprocable in a cylinder 19 of a reversible elevating piston and cylinder assemblage. The cylinder 19 is supported by a suitable' support 20 on the base 2 of the frame 1 and extends in an upright position so that by admission of fluid pressure to the lower end of the cylinder, the bridge or member 4 can be lifted. Suitable guides 22 are provided on the bridge 4 and are slidable in suitable guideways or bores 23 in guide members 24 which are secured in fixed position relative to the table 3 with their axes upright.

' It is desirable that the sheet be loaded while out of contact with the bridge 4 so as not to be scuffed thereagainst. Also it is desirable that the sheet be brought into contact with at least the mid-portion of the bridge 4 before it is stretched. In fact, it is preferable -to let it be so engaged before there is any appreciable tensioning force endwise of the sheet.

Consequently the jaws S and the bridge 4 must be operated in proper timed relation to each other.

In order that this simplified timed relation in driving the jaws 5 in relation to the bridge 4 be obtained without the necessity for power means other than the hydraulic piston and cylinder assemblage heretofore described, the jaws are drivingly connected to the piston and cylinder assemblage. For this purpose, each of the supports 9 is connected by a pivot 27 to a suitable gusset 28 on the table 3 for rocking about an axis extending transversely of the tensioning dimension. Mounted on the frame 1 by means of a suitable pivot 29 is a rock lever 30. The rock i lever 30 is pivotally connected at one end of a link 32 by means of a pivot 33. The opposite end of the link 32 is connected by a pivot 34 to the support 9 of the head 5.

At its opposite end, the rock lever 30 is connected by a pivot 36 to one end of a link 37. The opposite end of the link 37 is connected by a pivot 38, through the bridge 4, to the piston and cylinder assemblage so that the pivot 38 moves in fixed relation to the movement of the piston 18.

With this arrangement it is apparent that as the bridge 4 is moved upwardly by movement of the piston 18 toward extended position, the link 37 swings the left end of lthe rock lever upwardly and the right end of the lever 30 downwardly, so as to exert a downward pull Ithrough 3 the link 32 on the support 9 of the jaw 15. This rocks the support 9 about its pivot 27 in a direction outwardly from the mid-portion of the bridge 4 and downwardly, thus causing the sheet rst to engage the mid-portion of the bridge and then be stretched endwise as the head 5 is progressively swung downwardly and outwardly.

The downward movement of the heads 5 is such that no abrupt bends are formed in the sheet. Instead, the sheet becomes tangent to the upper face of the bridge 4 preferably before reaching the ends thereof in the tensioning dimension.

The operation and timing of the mechanism is dependent upon the links of those portions of the rocker 30 at opposite sides of its pivot 29, and the distance between the pivots 27 and 34. This distance can be selected for the particular effect desired. It is so chosen that theisheet is either untensioned, or so slightly tensioned as to be negligible, at the time the sheet is laid onto the crest of the bridge 4. Thereafter, the tension is increased beyond the elastic limit before an appreciable amount ofthe sheet is laid on the upper face of the bridge 4. This tensioning above the elastic limit is continued until the sheet is laid on the upper face of the bridge 4 to the extent necessary for stretch leveling.

It is found that with this type of operation, fluting does not start, and not having started at the time of initial stretching, does not develop later during the stretching operation. On the contrary, if no should stretch a sheet before the central portion reaches the bridge, thus forming wrinkles and uting, it is almost impossible to remove these by continued stretching.

The critical feature is that the fluting is eliminated at the inception.

Usually a machine of `the type described is one made for a very limited number of sizes and for high production. However, a certain amount of adjustment is readily obtainable; for example, by fastening the support 9 with the pivot 27 closer to, or removed from, the bridge 4. This can be done without appreciable change in the structure as the links 32 and 37 can be swung about their lower pivots 33 and 36 to compensate for some changes in the location of the pivot 27.

Again, the jaws may be mounted on the support 9 in different positions endwise thereof. Additional adjustment can be made by adjusting the length of the rocker 30, or by providing rockers of different lengths, depending upon the effects desired.

In the form illustrated, the gusset or flange 28, may be adjusted endwise of the frame, a plurality of bolt holes being arranged on the frame for this purpose. Likewise, the gusset 41 which supports the pivot 29 may be removed and bolted or welded at a diiferent position along the table 3 in a tensioning direction.

Thus the machine is highly flexible for a range of adjustments to meet conditions wherein a rapid changeover is not so important, but wherein a large number of parts are to be made for a single setting of the machine.

As illustrated in FIG. 2, the head 5 at the right of the machine is shown in a loading position with the bridge 4 also shown in the position which it occupies during loading of the sheet in the heads. The bridge S at the left-hand end of the machine is -the same as the bridge 5, and is operated in like manner, and the left-hand jaw 5 and left portion of the lbridge 4 are shown in the position which they assume at the end of the stretching operation.

It is to be noted that, in the stretched condition, the sheet S is tangent to the face of the bridge 4 and is not bent down at any sharp angle around the ends of the bridge 4.

Having thus described my invention, I claim:

1. A stretching machine comprising:

a frame;

ia die support;

poiwer means for raising and lowering the support relative to the frame;

stretch Yheads at two opposite ends of the die;

pivot means supporting at least one of the heads on the frame for rocking toward and aiway from the support about a horizontal axis extending forwardly and rearwardly of the frame;

power transmission means comprising rock lever means pivotally mounted on the frame for rocking about an axis parallel to said horizontal axis;

connecting means drivingly connecting said rock lever means, at opposite sides of the rocking axis of said rock lever means, to said one head and to the power means, respectively, for rocking said one head relative t-o the frame about said horizontal axis in fixed relation to the raising and lowering of the support by the power means.

2. A structure according to claim 1 wherein a male die is carried on said support and is convex upwardly;

said pivot means is so positioned on the frame that said one head rocks in an arcuate path which is concave toward the die;

and said transmission means is so related to power means and support as to cause a sheet of stock gripped by the heads to engage the highest portion of said die prior to exerting on the sheet sufficient tension to cause uting of the sheet.

3. A structure according to claim 1 wherein the connecting means comprise links.

4. A structure according to claim 1 :wherein the power transmission means comprise a pair of coaxial yrock levers of equal length arranged at the front and rear of the frame, respectively;

links connect the levers, respectively, at their inner ends, adjacent the die support, to said support and thereby to the power means; and

additional links connect the levers, respectively, at their outer ends, to said one head.

5. A structure according to claim 1 wherein the other head is also supported on the frame for rocking about an axis parallel to the rocking axis of the one head, a second rock lever means is pivotally mounted on the frame for rocking about an axis parallel to the rocking vaxis of the rst mentioned rock lever means; and

second connecting means drivingly connect said second rock lever means, at opposite sides of the rocking axis of said second rock lever means to said other head for rocking said other head about its axis relative to the frame in fixed relation to the raising and lowering of the support by the power means.

6. A structure according to claim 5 wherein the transmission means are arranged so that said heads are rocked in unison like distances toward the support concurrently and away from the support concurrently.

IReferences Cited UNITED STATES PATENTS RONALD D. GREFE, Primary Examiner.

U.S. Cl. X.R. 7.2-298, 305 

